Quoting from the article:

   TimeoutStopSec=0

That's cost me more than one hard power button powerdon (on a desktop machine with the system partition on SSD - unnerving).

One of the innumerable things that systemd stops on shutdown gets stuck - permanently - and the machine goes into a state out of which, to my knowledge, is only a powerdown or reset.

I ended up searching for the above and replacing them with a reasonable timeout (several minutes).